diff --git a/index.ts b/index.ts
index 7185e16..33b09a3 100644
--- a/index.ts
+++ b/index.ts
@@ -15,6 +15,8 @@ import { FabricClient } from './src/fabric-client.js';
 import { IdentityRegistry } from './src/identity.js';
 import { syncFabricCommands } from './src/command-sync.js';
 import { PresenceSync } from './src/presence-sync.js';
+import { SubDiscussionStore } from './src/sub-discussion-store.js';
+import { registerSubDiscussionHook } from './src/sub-discussion-hook.js';
 import path from 'node:path';
 import os from 'node:os';
 
@@ -48,19 +50,38 @@ export default defineChannelPluginEntry({
       on: (ev: string, fn: (...args: unknown[]) => unknown) => void;
       registerTool: (d: unknown) => void;
     };
-    const cfg = (api.config ?? {}) as { channels?: { fabric?: { centerApiBase?: string } } };
+    const cfg = (api.config ?? {}) as {
+      channels?: { fabric?: { centerApiBase?: string; commandsSyncKey?: string } };
+    };
     const centerApiBase = cfg.channels?.fabric?.centerApiBase ?? 'http://localhost:7001/api';
     const idFile =
       api.pluginConfig?.identityFilePath ??
       path.join(os.homedir(), '.openclaw', 'fabric-identity.json');
+    const subDiscussionFile = path.join(
+      os.homedir(),
+      '.openclaw',
+      'fabric-sub-discussion.json',
+    );
 
     // tools operate against a default Center; per-account keys come from config
     const client = new FabricClient(centerApiBase);
     const identity = new IdentityRegistry(idFile);
+    const subDiscussion = new SubDiscussionStore(subDiscussionFile);
     registerFabricTools(
       { registerTool: (d) => api.registerTool(d), logger: api.logger },
       client,
       identity,
+      subDiscussion,
+      cfg,
+    );
+    // Per-(agent, channel) prompt injection for sub-discussion channels.
+    // Runs as a sibling to PrismFacet's before_prompt_build hook (and
+    // ClawPrompts' fabric-chat-injector); openclaw composes
+    // appendSystemContext from all registered handlers.
+    registerSubDiscussionHook(
+      { on: api.on, logger: api.logger },
+      subDiscussion,
+      identity,
     );
 
     // Cross-plugin API: globalThis.__fabric
diff --git a/openclaw.plugin.json b/openclaw.plugin.json
index 21ac613..8218aa9 100644
--- a/openclaw.plugin.json
+++ b/openclaw.plugin.json
@@ -14,7 +14,9 @@
       "create-work-channel",
       "create-report-channel",
       "create-discussion-channel",
+      "create-sub-discussion",
       "discussion-complete",
+      "close-sub-discussion",
       "fabric-canvas",
       "fabric-channel",
       "fabric-send-message",
diff --git a/src/sub-discussion-hook.ts b/src/sub-discussion-hook.ts
new file mode 100644
index 0000000..7ff6479
--- /dev/null
+++ b/src/sub-discussion-hook.ts
@@ -0,0 +1,76 @@
+import type { IdentityRegistry } from './identity.js';
+import type { SubDiscussionStore } from './sub-discussion-store.js';
+
+// Plugin-local before_prompt_build hook that injects per-(agent, channel)
+// guides for sub-discussion channels created via the `create-sub-discussion`
+// tool. Mirrors the pattern used by ClawPrompts' fabric-chat-injector
+// (channelId-aware injection) but with content dynamically supplied at
+// channel-creation time instead of read from static files via PrismFacet's
+// router/rule registry.
+//
+// Match logic per turn:
+//   ctx.channelId  → store.find()  → sub-discussion entry
+//   ctx.agentId    → identity.findByAgentId().fabricUserId
+//                    ─ matches entry.hostUserId   → inject hostGuide
+//                    ─ matches entry.guestUserIds → inject guestGuide
+//                    ─ neither                    → no injection
+//
+// Fail-closed on unknown agentId/channelId — we never inject "the wrong"
+// guide, only the right one or nothing.
+
+const _G = globalThis as Record<string, unknown>;
+const DEDUP_KEY = '_fabricSubDiscussionHookDedup';
+
+type PromptCtx = {
+  agentId?: string;
+  channelId?: string;
+  messageProvider?: string;
+};
+
+export function registerSubDiscussionHook(
+  api: {
+    on: (hook: string, handler: (...args: unknown[]) => unknown) => void;
+    logger: { info: (m: string) => void; warn: (m: string) => void };
+  },
+  store: SubDiscussionStore,
+  identity: IdentityRegistry,
+): void {
+  if (!(_G[DEDUP_KEY] instanceof WeakSet)) _G[DEDUP_KEY] = new WeakSet<object>();
+  const dedup = _G[DEDUP_KEY] as WeakSet<object>;
+
+  api.on('before_prompt_build', async (...args: unknown[]) => {
+    const event = args[0];
+    const ctx = (args[1] ?? {}) as PromptCtx;
+    // The hook fires both for fabric-driven turns (channelId set) and
+    // for other triggers (HF wake, exec-event, etc.) — drop those.
+    if (typeof event === 'object' && event !== null) {
+      if (dedup.has(event)) return undefined;
+      dedup.add(event);
+    }
+    const agentId = (ctx.agentId ?? '').trim();
+    const channelId = (ctx.channelId ?? '').trim();
+    if (!agentId || !channelId) return undefined;
+    const provider = (ctx.messageProvider ?? '').toLowerCase();
+    if (provider && provider !== 'fabric') return undefined;
+
+    const entry = store.find(channelId);
+    if (!entry) return undefined;
+
+    const ident = identity.findByAgentId(agentId);
+    const myUserId = (ident?.fabricUserId ?? '').trim();
+    if (!myUserId) {
+      // identity registry caches fabricUserId after the first agentLogin
+      // in inbound.ts. If it's missing here, the agent likely hasn't
+      // completed login yet — skip rather than guess.
+      return undefined;
+    }
+
+    if (myUserId === entry.hostUserId) {
+      return { appendSystemContext: entry.hostGuide };
+    }
+    if (entry.guestUserIds.includes(myUserId)) {
+      return { appendSystemContext: entry.guestGuide };
+    }
+    return undefined;
+  });
+}
diff --git a/src/sub-discussion-store.ts b/src/sub-discussion-store.ts
new file mode 100644
index 0000000..b0740ea
--- /dev/null
+++ b/src/sub-discussion-store.ts
@@ -0,0 +1,76 @@
+import { readFileSync, writeFileSync, existsSync, mkdirSync } from 'node:fs';
+import { dirname } from 'node:path';
+
+// Records per-(sub-discussion-channel) state created by the
+// `create-sub-discussion` tool and consumed by:
+//   1. `before_prompt_build` hook — looks up by (agentId, channelId) to
+//      inject the host or guest guide as appendSystemContext.
+//   2. `close-sub-discussion` tool — looks up by sub channelId to find
+//      the parent channel to post the callback to and to validate that
+//      the caller is the original host.
+//
+// One sub-discussion = one channel. Lifetime: from create-sub-discussion
+// return until close-sub-discussion (or gateway-stop / disk corruption).
+// We persist to a small JSON file so a gateway restart mid-interview
+// doesn't strand both host and guest with no guide.
+
+export type SubDiscussionEntry = {
+  subChannelId: string;
+  hostAgentId: string;         // the openclaw agentId that called create-sub-discussion
+  hostUserId: string;          // the host's Fabric Center userId (session.user.id)
+  guestUserIds: string[];      // Fabric Center userIds invited as guests
+  hostGuide: string;           // appended to host's session system prompt while in this channel
+  guestGuide: string;          // appended to each guest's session system prompt while in this channel
+  callbackGuildNodeId: string; // where to post the callback when close is called
+  callbackChannelId: string;   // parent channel to post callback to (system msg)
+  createdAt: string;           // ISO timestamp
+};
+
+type StoreFile = { entries: SubDiscussionEntry[] };
+
+export class SubDiscussionStore {
+  private byChannelId = new Map<string, SubDiscussionEntry>();
+
+  constructor(private readonly filePath: string) {
+    this.load();
+  }
+
+  private load(): void {
+    if (!existsSync(this.filePath)) return;
+    try {
+      const data = JSON.parse(readFileSync(this.filePath, 'utf8')) as StoreFile;
+      for (const e of data.entries ?? []) {
+        if (e?.subChannelId) this.byChannelId.set(e.subChannelId, e);
+      }
+    } catch {
+      // Corrupt file → start empty; first mutation rewrites cleanly.
+    }
+  }
+
+  private persist(): void {
+    mkdirSync(dirname(this.filePath), { recursive: true });
+    const data: StoreFile = { entries: [...this.byChannelId.values()] };
+    writeFileSync(this.filePath, JSON.stringify(data, null, 2));
+  }
+
+  list(): SubDiscussionEntry[] {
+    return [...this.byChannelId.values()];
+  }
+
+  find(subChannelId: string): SubDiscussionEntry | undefined {
+    return this.byChannelId.get(subChannelId);
+  }
+
+  add(entry: SubDiscussionEntry): void {
+    this.byChannelId.set(entry.subChannelId, entry);
+    this.persist();
+  }
+
+  remove(subChannelId: string): SubDiscussionEntry | undefined {
+    const e = this.byChannelId.get(subChannelId);
+    if (!e) return undefined;
+    this.byChannelId.delete(subChannelId);
+    this.persist();
+    return e;
+  }
+}
diff --git a/src/tools.ts b/src/tools.ts
index 5d7f018..a1d2806 100644
--- a/src/tools.ts
+++ b/src/tools.ts
@@ -1,5 +1,7 @@
 import type { FabricClient } from './fabric-client.js';
 import type { IdentityRegistry } from './identity.js';
+import type { SubDiscussionStore } from './sub-discussion-store.js';
+import { resolveCommandsSyncKey } from './accounts.js';
 
 // OpenClaw tool registration api (loose typing — concrete shape from
 // openclaw/plugin-sdk/core at host SDK version).
@@ -10,6 +12,9 @@ type ToolApi = {
 
 type Ctx = { agentId?: string };
 
+// Loose config shape — just the fields we read here.
+type ToolsCfg = { channels?: { fabric?: { commandsSyncKey?: string } }; [k: string]: unknown };
+
 const X_BY_KIND: Record<string, string> = {
   chat: 'general',
   work: 'work',
@@ -17,10 +22,25 @@ const X_BY_KIND: Record<string, string> = {
   discussion: 'discuss',
 };
 
+// Delay between create-sub-discussion's channel create and greeting post.
+// Backend pushes channel.joined to invitee sockets on create; that push
+// has to traverse socket.io rooms before the guest plugin can sub the
+// channel:<id> room. If the greeting is posted before that, the guest's
+// turn-activation wakeup misses (the socket isn't in the room yet).
+// 500ms is empirically slack enough on local sim + production t3, and
+// short enough not to feel laggy from the host's tool-result POV. Bump
+// via FABRIC_SUB_DISCUSSION_GREETING_DELAY_MS env if needed.
+const GREETING_DELAY_MS = (() => {
+  const v = Number.parseInt(process.env.FABRIC_SUB_DISCUSSION_GREETING_DELAY_MS ?? '', 10);
+  return Number.isFinite(v) && v >= 0 ? v : 500;
+})();
+
 export function registerFabricTools(
   api: ToolApi,
   client: FabricClient,
   identity: IdentityRegistry,
+  store: SubDiscussionStore,
+  cfg: ToolsCfg,
 ): void {
   // Resolve the calling agent's Fabric session + a guild's token/endpoint.
   const ctxGuild = async (agentId: string, guildNodeId: string) => {
@@ -134,6 +154,245 @@ export function registerFabricTools(
     },
   }));
 
+  // ───────────────────────────────────────────────────────────────────
+  // create-sub-discussion: open a discuss-type sub-channel hanging off
+  // the caller's current channel. Designed for host-driven multi-turn
+  // exchanges (interview, brainstorm, narrow Q&A) where the guests are
+  // either fresh agents without workflow capability (recruitment
+  // interviewee) or peers that just need a short scoped chat without
+  // entering their own subflow.
+  //
+  // What it does on top of plain create-discussion-channel:
+  //   1. Persists a store entry indexed by the new sub channelId, carrying:
+  //        host agent + userId, guest userIds, host/guest guide texts,
+  //        callback (parent) channel info.
+  //   2. Auto-posts `greetingMsg` using the host's own Fabric account so
+  //      turn rotation's activation rule (first author → newOrder[0],
+  //      currentSpeaker → newOrder[1], wakeup → newOrder[1]) puts the
+  //      first guest on the spot immediately — no race where host posts
+  //      before guest's socket subs the channel room (we wait
+  //      GREETING_DELAY_MS for backend's channel.joined push to land).
+  //   3. The accompanying before_prompt_build hook (sub-discussion-hook
+  //      registered from index.ts) then injects `hostGuideMsg` into the
+  //      host's session prompt and `guestGuideMsg` into each guest's
+  //      session prompt whenever a turn in this channel fires — so the
+  //      two roles see different instructions, no shared guide file.
+  // ───────────────────────────────────────────────────────────────────
+  api.registerTool((ctx: Ctx) => ({
+    name: 'create-sub-discussion',
+    description:
+      'Open a host-driven sub-discussion channel (x_type=discuss) hanging off your current channel, ' +
+      'with role-specific system-prompt guides for host and guests. Use this for interviews / scoped ' +
+      'Q&A where you stay in control of when the conversation ends. Returns the sub channelId; ' +
+      'reach it via fabric-send-message in the rotating turn order. Close with close-sub-discussion ' +
+      'to write a callback back into the parent channel.',
+    parameters: {
+      type: 'object',
+      additionalProperties: false,
+      required: [
+        'guildNodeId',
+        'currentChannelId',
+        'channelName',
+        'greetingMsg',
+        'hostGuideMsg',
+        'guestGuideMsg',
+        'guests',
+      ],
+      properties: {
+        guildNodeId: { type: 'string', description: 'Fabric guild node id (same guild for parent + sub).' },
+        currentChannelId: {
+          type: 'string',
+          description: 'Channel id you are currently in (parent). Used as the callback target on close.',
+        },
+        channelName: { type: 'string', description: 'Display name for the new sub-discussion channel.' },
+        greetingMsg: {
+          type: 'string',
+          description:
+            'First message posted by YOU (the host) in the sub channel. Triggers turn rotation so ' +
+            "the first guest's session wakes immediately with both your greeting in history and the " +
+            'guest guide injected as system prompt.',
+        },
+        hostGuideMsg: {
+          type: 'string',
+          description:
+            "Appended to YOUR session's system prompt whenever a turn fires in this sub channel. " +
+            'Use it to remind yourself of the procedure (what to ask, when to call close-sub-discussion).',
+        },
+        guestGuideMsg: {
+          type: 'string',
+          description:
+            "Appended to EACH GUEST's session system prompt for turns in this sub channel. Use it to " +
+            'orient guests with no prior workflow context (e.g. a fresh interviewee). Keep it short; ' +
+            'long guides bloat every turn.',
+        },
+        guests: {
+          type: 'array',
+          items: { type: 'string' },
+          minItems: 1,
+          description:
+            'Fabric Center userIds invited as guests. Resolve via fabric-channel-list members or the ' +
+            '<name>@<role>.hangman-lab.top email convention.',
+        },
+        purpose: { type: 'string', description: 'Optional channel.purpose for discoverability.' },
+      },
+    },
+    execute: async (
+      _id: string,
+      p: {
+        guildNodeId: string;
+        currentChannelId: string;
+        channelName: string;
+        greetingMsg: string;
+        hostGuideMsg: string;
+        guestGuideMsg: string;
+        guests: string[];
+        purpose?: string;
+      },
+    ) => {
+      const agentId = ctx.agentId;
+      if (!agentId) return { ok: false, error: 'no agent context' };
+      if (!Array.isArray(p.guests) || p.guests.length === 0) {
+        return { ok: false, error: 'guests must be a non-empty array of Fabric userIds' };
+      }
+      const { session, guild, token } = await ctxGuild(agentId, p.guildNodeId);
+      const ch = await client.createChannel(guild.endpoint, token, {
+        guildId: p.guildNodeId,
+        name: p.channelName,
+        xType: 'discuss',
+        isPublic: false,
+        memberUserIds: p.guests,
+        ...(p.purpose !== undefined ? { purpose: p.purpose } : {}),
+      });
+      store.add({
+        subChannelId: ch.id,
+        hostAgentId: agentId,
+        hostUserId: session.user.id,
+        guestUserIds: [...p.guests],
+        hostGuide: p.hostGuideMsg,
+        guestGuide: p.guestGuideMsg,
+        callbackGuildNodeId: p.guildNodeId,
+        callbackChannelId: p.currentChannelId,
+        createdAt: new Date().toISOString(),
+      });
+      // Let backend's channel.joined push reach guest sockets before our
+      // greeting fires — otherwise the wakeup emitted by turn-activation
+      // races a not-yet-subscribed socket.io room.
+      if (GREETING_DELAY_MS > 0) {
+        await new Promise((r) => setTimeout(r, GREETING_DELAY_MS));
+      }
+      try {
+        await client.postMessage(guild.endpoint, token, ch.id, p.greetingMsg, session.user.id);
+      } catch (err) {
+        api.logger.warn(
+          `fabric: create-sub-discussion greeting post failed channel=${ch.id} err=${String(err)}`,
+        );
+      }
+      return { ok: true, subChannelId: ch.id };
+    },
+  }));
+
+  // ───────────────────────────────────────────────────────────────────
+  // close-sub-discussion: post a system-authored callback into the
+  // parent channel + close the sub-discussion channel. Only the original
+  // host can call this. Uses the Guild's x-fabric-system-key path (shared
+  // secret = commandsSyncKey) so the callback lands as a guild/system
+  // author, not the host's personal account — and can wake the host on
+  // the parent channel to continue whatever workflow opened the sub.
+  // ───────────────────────────────────────────────────────────────────
+  api.registerTool((ctx: Ctx) => ({
+    name: 'close-sub-discussion',
+    description:
+      'Close a sub-discussion channel you opened (host-only) and write a callback to the parent ' +
+      'channel as a system message. Pass `wakeupHost: false` to land the callback silently in ' +
+      'history without waking yourself.',
+    parameters: {
+      type: 'object',
+      additionalProperties: false,
+      required: ['subChannelId', 'callbackMsg'],
+      properties: {
+        subChannelId: { type: 'string', description: 'The sub-discussion channelId returned by create-sub-discussion.' },
+        callbackMsg: {
+          type: 'string',
+          description:
+            'Content to post into the parent channel as a system-authored message. Typical content: ' +
+            'the conclusion / extracted data from the sub-discussion, so the next turn on the parent ' +
+            'channel can act on it.',
+        },
+        wakeupHost: {
+          type: 'boolean',
+          description:
+            'Whether to wake YOU (the host) on the parent channel. Default true — for recruitment ' +
+            'interview flow where the next workflow step needs to run immediately. Pass false for ' +
+            'fire-and-forget logging.',
+        },
+      },
+    },
+    execute: async (
+      _id: string,
+      p: { subChannelId: string; callbackMsg: string; wakeupHost?: boolean },
+    ) => {
+      const agentId = ctx.agentId;
+      if (!agentId) return { ok: false, error: 'no agent context' };
+      const entry = store.find(p.subChannelId);
+      if (!entry) {
+        return { ok: false, error: `sub-discussion not found: ${p.subChannelId}` };
+      }
+      if (entry.hostAgentId !== agentId) {
+        return {
+          ok: false,
+          error: `only the host (${entry.hostAgentId}) may close this sub-discussion`,
+        };
+      }
+      const systemKey = resolveCommandsSyncKey(cfg);
+      if (!systemKey) {
+        return {
+          ok: false,
+          error:
+            'channels.fabric.commandsSyncKey is not configured — close-sub-discussion needs it for ' +
+            'the x-fabric-system-key callback. Configure via openclaw config.',
+        };
+      }
+      const { guild, token } = await ctxGuild(agentId, entry.callbackGuildNodeId);
+      const wakeup = p.wakeupHost !== false;
+      // 1) Post callback into parent channel via the system-key path.
+      const url = `${guild.endpoint}/api/channels/${encodeURIComponent(entry.callbackChannelId)}/messages`;
+      const res = await fetch(url, {
+        method: 'POST',
+        headers: {
+          'content-type': 'application/json',
+          'x-fabric-system-key': systemKey,
+        },
+        body: JSON.stringify({
+          content: p.callbackMsg,
+          wakeupUserId: wakeup ? entry.hostUserId : null,
+        }),
+      }).catch((err) => {
+        throw new Error(`callback POST failed: ${String(err)}`);
+      });
+      if (!res.ok) {
+        const text = await res.text().catch(() => '');
+        return {
+          ok: false,
+          error: `callback POST ${url} -> ${res.status} ${text}`,
+        };
+      }
+      // 2) Close the sub channel using the host's own bearer (the host is
+      // a member of the channel — channel.close auth is per-member).
+      try {
+        await client.closeChannel(guild.endpoint, token, entry.subChannelId);
+      } catch (err) {
+        api.logger.warn(
+          `fabric: close-sub-discussion: sub channel close failed channel=${entry.subChannelId} err=${String(err)}`,
+        );
+      }
+      // 3) Drop the store entry so the prompt-injection hook stops firing
+      // for this channel (the sub is closed; any straggler turns would
+      // just hit the closed-channel write reject downstream).
+      store.remove(entry.subChannelId);
+      return { ok: true, closed: true };
+    },
+  }));
+
   // fabric-canvas: share / update / read / close the channel's single
   // pinned canvas document (one tool, four actions). update/close are
   // sharer-only server-side (the guild returns 403 otherwise).